三道关于高一三角函数的题目1)求值cos(π/5)cos(2π/5)2)求函数y=1-(cosx)^2+(cosx)^4的最小正周期3)求函数y=2sinx(sinx+cosx)的减区间1)0.252)π/43)[kπ+3/8π,kπ+7/8π]

Question

三道关于高一三角函数的题目
1)求值cos(π/5)cos(2π/5)
2)求函数y=1-(cosx)^2+(cosx)^4的最小正周期
3)求函数y=2sinx(sinx+cosx)的减区间
1)0.25 2)π/4 3)[kπ+3/8π,kπ+7/8π]

Answer 1

1)1/4∵cos(π/5)cos(2π/5)+sin(π/5)sin(2π/5)=cos(π/5)cos(π/5)cos(2π/5)-sin(π/5)sin(2π/5)=cos(3π/5)∴cos(π/5)cos(2π/5)=[cos(π/5)+cos(3π/5) ]/2又∵cos(π/5)+cos(3π/5)=cos(π/5)-cos(2π/5)co...